More xml woes

I have the following in my config file :

Code:

---

<configuration>
  <appSettings>
      <add key="ServerIPAddress" value="127.0.0.14444" />
  </appSettings>
</configuration>

---

To update the node I use the following :

Code:

---

Dim doc As New XmlDocument()
configName = "myconfig.config"
doc.Load(configName )

'ServerIPAddress
Dim elServerIPAddress As XmlElement = DirectCast(doc.SelectSingleNode("/configurationappSettingsadd[@key='ServerIPAddress']"), XmlElement)
If elServerIPAddress IsNot Nothing Then
    elServerIPAddress.SetAttribute("value", Me.txtServerIP.Text)
End If

---

Which works fine but what I want to know is :

If the node does not exist how do I create it ?

Thanks in Advance folks :-)